68,305 research outputs found
Diagnosis and treatment of hereditary hemorrhagic telangiectasia in a pediatric patient with chronic cyanosis.
Background:
Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant disorder of vascular dysplasias that is characterized by mucocutaneous telangiectasias, gastrointestinal tract bleeding, and arteriovenous malformations (AVMs) of the pulmonary, hepatic, and cerebral vascular systems.
Case Summary:
A seven-year-old boy presented to his primary care provider with a five-day history of watery diarrhea and was incidentally found to have oxygen saturations in the low eighties, perioral cyanosis, and clubbing on physical exam. He was referred to the pediatric emergency department (ED) for evaluation. Upon presentation to the pediatric ED, oxygen saturation ranged from 74-85%. He was in no acute distress and was afebrile with normal vital signs. The patient was small for his age with height and weight in the thirteenth and third percentiles, respectively, and had central cyanosis and clubbing of fingers and toes. Auscultation revealed diminished lung sounds in the right lower lobe. No mucocutaneous telangiectasias or cardiac murmurs were appreciated. Family history was positive for hereditary hemorrhagic telangiectasia (HHT) with gastrointestinal bleeding and anemia in his maternal great grandmother and maternal grandmother, minor bleeding and mucocutaneous telangiectasias in his mother, and cyanosis with exercise and recurrent epistaxis in his brother.
Complete blood count was significant for a hemoglobin level of 18.1 g/dL. A chest x-ray (Figure 1) showed an airspace opacification within the superior segment of the right lower lobe suspicious for an arteriovenous malformation (AVM).peer-reviewe
Limits on the temporal variation of the fine structure constant, quark masses and strong interaction from quasar absorption spectra and atomic clock experiments
We perform calculations of the dependence of nuclear magnetic moments on
quark masses and obtain limits on the variation of from
recent measurements of hydrogen hyperfine (21 cm) and molecular rotational
transitions in quasar absorption systems, atomic clock experiments with
hyperfine transitions in H, Rb, Cs, Yb, Hg and optical transition in
Hg. Experiments with Cd, deuterium/hydrogen, molecular SF and
Zeeman transitions in He/Xe are also discussed.Comment: 8 pages, 1 figure, uses revtex
The Sigma Commutator from Lattice QCD
As a direct source of information on chiral symmetry breaking within QCD, the
sigma commutator is of considerable importance. Since hadron structure is a
non-perturbative problem, numerical calculations on a space-time lattice are
currently the only rigorous approach. With recent advances in the calculation
of hadron masses within full QCD, it is of interest to see whether the sigma
commutator can be calculated directly from the dependence of the nucleon mass
on the input quark mass. We show that, provided the correct chiral behaviour of
QCD is respected in the extrapolation to realistic quark masses, one can indeed
obtain a fairly reliable determination of the sigma commutator using present
lattice data. For two-flavour dynamical fermion QCD the sigma commutator lies
between 45 and 55 MeV based on recent data from CP-PACS and UKQCD.Comment: 4 pages, 3 figures, uses espcrc1.sty and epsfig.sty. Contribution to
the proceedings of the International Conference on Quark Nuclear Physics held
in Adelaide Feb. 200
Chiral Corrections to Baryon Masses Calculated within Lattice QCD
Consideration of the analytic properties of pion-induced baryon self energies
leads to new functional forms for the extrapolation of light baryon masses.
These functional forms reproduce the leading non-analytic behavior of chiral
perturbation theory, the correct non-analytic behavior at the threshold
and the appropriate heavy-quark limit. They involve only three unknown
parameters, which may be obtained by fitting lattice QCD data. Recent dynamical
fermion results from CP-PACS and UKQCD are extrapolated using these new
functional forms. We also use these functions to probe the limit of
applicability of chiral perturbation theory.Comment: 4 pages, 2 figures, Contribution to the Proceedings of the 15th
Particles and Nuclei International Conference (PANIC 99), Uppsala, Sweden,
June 10-16, 199
Calculation of disease dynamics in a population of households
Early mathematical representations of infectious disease dynamics assumed a single, large, homogeneously mixing population. Over the past decade there has been growing interest in models consisting of multiple smaller subpopulations (households, workplaces, schools, communities), with the natural assumption of strong homogeneous mixing within each subpopulation, and weaker transmission between subpopulations. Here we consider a model of SIRS (susceptible-infectious-recovered-suscep​tible) infection dynamics in a very large (assumed infinite) population of households, with the simplifying assumption that each household is of the same size (although all methods may be extended to a population with a heterogeneous distribution of household sizes). For this households model we present efficient methods for studying several quantities of epidemiological interest: (i) the threshold for invasion; (ii) the early growth rate; (iii) the household offspring distribution; (iv) the endemic prevalence of infection; and (v) the transient dynamics of the process. We utilize these methods to explore a wide region of parameter space appropriate for human infectious diseases. We then extend these results to consider the effects of more realistic gamma-distributed infectious periods. We discuss how all these results differ from standard homogeneous-mixing models and assess the implications for the invasion, transmission and persistence of infection. The computational efficiency of the methodology presented here will hopefully aid in the parameterisation of structured models and in the evaluation of appropriate responses for future disease outbreaks
A model of large-scale proteome evolution
The next step in the understanding of the genome organization, after the
determination of complete sequences, involves proteomics. The proteome includes
the whole set of protein-protein interactions, and two recent independent
studies have shown that its topology displays a number of surprising features
shared by other complex networks, both natural and artificial. In order to
understand the origins of this topology and its evolutionary implications, we
present a simple model of proteome evolution that is able to reproduce many of
the observed statistical regularities reported from the analysis of the yeast
proteome. Our results suggest that the observed patterns can be explained by a
process of gene duplication and diversification that would evolve proteome
networks under a selection pressure, favoring robustness against failure of its
individual components
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