74 research outputs found
Perturbations of a Stringy Black Hole
We extend the three dimensional stringy black hole of Horne and Horowitz to
four dimensions. After a brief discussion of the global properties of the
metric, we discuss the stability of the background with respect to small
perturbations, following the methods of Gilbert and of Chandrasekhar. The
potential for axial perturbations is found to be positive definite.Comment: 15
Asymptotic Behavior of 2-d Black Holes
We consider the solutions of the field equations for the large dilaton
gravity model in dimensions recently proposed by Callan, Giddings, Harvey
and Strominger (CGHS). We find time dependant solutions with finite mass and
vanishing flux in the weak coupling regime, as well as solutions which lie
entirely in the Liouville region.Comment: 10 page
Tachyon Condensates and String Theoretic Inflation
Cosmological solutions of the beta function equations for the background
fields of the closed bosonic string are investigated at the one-loop level.
Following recent work of Kostelecky and Perry, it is assumed that the spatial
sections of the space-time are conformally flat. Working in the sigma-model
frame, the non-trivial tachyon potential is utilized to determine solutions
with sufficient inflation to solve the smoothness and flatness problems. The
graceful exit and density perturbation constraints can also be successfully
implemented.Comment: FERMI-PUB 93/074-T, harvmac, 16 page
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Ecologies, synergies, and biological systems shaping human milk composition—a report from “Breastmilk Ecology: Genesis of Infant Nutrition (BEGIN)” Working Group 2
Human milk is universally recognized as the preferred food for infants during the first 6 mo of life because it provides not only essential and conditionally essential nutrients in necessary amounts but also other biologically active components that are instrumental in protecting, communicating important information to support, and promoting optimal development and growth in infants. Despite decades of research, however, the multifaceted impacts of human milk consumption on infant health are far from understood on a biological or physiological basis. Reasons for this lack of comprehensive knowledge of human milk functions are numerous, including the fact that milk components tend to be studied in isolation, although there is reason to believe that they interact. In addition, milk composition can vary greatly within an individual as well as within and among populations. The objective of this working group within the Breastmilk Ecology: Genesis of Infant Nutrition (BEGIN) Project was to provide an overview of human milk composition, factors impacting its variation, and how its components may function to coordinately nourish, protect, and communicate complex information to the recipient infant. Moreover, we discuss the ways whereby milk components might interact such that the benefits of an intact milk matrix are greater than the sum of its parts. We then apply several examples to illustrate how milk is better thought of as a biological system rather than a more simplistic “mixture” of independent components to synergistically support optimal infant health
Cosmological Evolution of a Brane Universe in a Type 0 String Background
We study the cosmological evolution of a D3-brane Universe in a type 0 string
background. We follow the brane-universe along the radial coordinate of the
background and we calculate the energy density which is induced on the brane
because of its motion in the bulk. We find that for some typical values of the
parameters and for a particular range of values of the scale factor of the
brane-universe, the effective energy density is dominated by a term
proportional to indicating a slow varying inflationary
phase. For larger values of the scale factor the effective energy density takes
a constant value and the brane-universe enters its usual inflationary period.Comment: 25 pages,1 figure,LaTex file,final version to appear in Phys. Rev.
Lactation and neonatal nutrition: defining and refining the critical questions.
This paper resulted from a conference entitled "Lactation and Milk: Defining and refining the critical questions" held at the University of Colorado School of Medicine from January 18-20, 2012. The mission of the conference was to identify unresolved questions and set future goals for research into human milk composition, mammary development and lactation. We first outline the unanswered questions regarding the composition of human milk (Section I) and the mechanisms by which milk components affect neonatal development, growth and health and recommend models for future research. Emerging questions about how milk components affect cognitive development and behavioral phenotype of the offspring are presented in Section II. In Section III we outline the important unanswered questions about regulation of mammary gland development, the heritability of defects, the effects of maternal nutrition, disease, metabolic status, and therapeutic drugs upon the subsequent lactation. Questions surrounding breastfeeding practice are also highlighted. In Section IV we describe the specific nutritional challenges faced by three different populations, namely preterm infants, infants born to obese mothers who may or may not have gestational diabetes, and infants born to undernourished mothers. The recognition that multidisciplinary training is critical to advancing the field led us to formulate specific training recommendations in Section V. Our recommendations for research emphasis are summarized in Section VI. In sum, we present a roadmap for multidisciplinary research into all aspects of human lactation, milk and its role in infant nutrition for the next decade and beyond
Back Reaction of Strings in Self-Consistent String Cosmology
We compute the string energy-momentum tensor and {\bf derive} the string
equation of state from exact string dynamics in cosmological spacetimes.
and -dimensional universes are treated for any expansion factor
. Strings obey the perfect fluid relation with
three different behaviours: (i) {\it Unstable} for with
growing energy density , {\bf negative} pressure, and ; (ii){\it Dual} for , with , {\bf positive} pressure and (as radiation); (iii) {\it
Stable} for with , {\bf vanishing}
pressure and (as cold matter). We find the back reaction effect
of these strings on the spacetime and we take into account the quantum string
decay through string splitting. This is achieved by considering {\bf
self-consistently} the strings as matter sources for the Einstein equations, as
well as for the complete effective string equations. String splitting
exponentially suppress the density of unstable strings for large . The
self-consistent solution to the Einstein equations for string dominated
universes exhibits the realistic matter dominated behaviour for large times and the radiation dominated behaviour for early times. De Sitter universe does not emerge as
solution of the effective string equations. The effective string action
(whatever be the dilaton, its potential and the central charge term) is not the
appropriate framework in which to address the question of string driven
inflation.Comment: 29 pages, revtex, LPTHE-94-2
The prevalence of obesity in children with autism: a secondary data analysis using nationally representative data from the National Survey of Children's Health
<p>Abstract</p> <p>Background</p> <p>The prevalence of childhood obesity has increased dramatically in the last two decades and numerous efforts to understand, intervene on, and prevent this significant threat to children's health are underway for many segments of the pediatric population. Understanding the prevalence of obesity in populations of children with developmental disorders is an important undertaking, as the factors that give rise to obesity may not be the same as for typically developing children, and because prevention and treatment efforts may need to be tailored to meet their needs and the needs of their families. The goal of the current study was to estimate the prevalence of obesity in children and adolescents with autism.</p> <p>Methods</p> <p>This study was a secondary data analysis of cross-sectional nationally representative data collected by telephone interview of parents/guardians on 85,272 children ages 3-17 from the 2003-2004 National Survey of Children's Health (NSCH). Autism was determined by response to the question, "Has a doctor or health professional ever told you that your child has autism?" Children and adolescents were classified as obese accordingto CDC guidelines for body mass index (BMI) for age and sex.</p> <p>Results</p> <p>The prevalence of obesity in children with autism was 30.4% compared to 23.6% of children without autism (p = .075). The unadjusted odds of obesity in children with autism was 1.42 (95% confidence interval (CI): 1.00, 2.02, p = .052) compared to children without autism.</p> <p>Conclusions</p> <p>Based on US nationally representative data, children with autism have a prevalence of obesity at least as high as children overall. These findings suggest that additional research is warranted to understand better the factors that influence the development of obesity in this population of children.</p
Irrational Conformal Field Theory
This is a review of irrational conformal field theory, which includes
rational conformal field theory as a small subspace. Central topics of the
review include the Virasoro master equation, its solutions and the dynamics of
irrational conformal field theory. Discussion of the dynamics includes the
generalized Knizhnik-Zamolodchikov equations on the sphere, the corresponding
heat-like systems on the torus and the generic world- sheet action of
irrational conformal field theory.Comment: 195 pages, Latex, 12 figures, to appear in Physics Reports. Typos
corrected in Sections 13 and 14, and a footnote added in Section 1
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