914 research outputs found
Modeling of Immunosenescence and Risk of Death from Respiratory Infections: Evaluation of the Role of Antigenic Load and Population Heterogeneity
It is well known that efficacy of immune functions declines with age. It results in an increase of severity and duration of respiratory infections and also in dramatic growth of risk of death due to these diseases after age 65. The goal of this work is to describe and investigate the mechanism underlying the age pattern of the mortality rate caused by infectious diseases and to determine the cause-specific hazard rate as a function of immune system characteristics. For these purposes we develop a three-compartment model explaining observed risk-of-death. The model incorporates up-to-date knowledge about cellular mechanisms of aging, disease dynamics, population heterogeneity in resistance to infections, and intrinsic aging rate. The results of modeling show that the age-trajectory of mortality caused by respiratory infections may be explained by the value of antigenic load, frequency of infections and the rate of aging of the stem cell population (i.e. the population of T-lymphocyte progenitor cells). The deceleration of infection-induced mortality at advanced age can be explained by selection of individuals with a slower rate of stem cell aging. Parameter estimates derived from fitting mortality data indicate that infection burden was monotonically decreasing during the twentieth century, and changes in total antigenic load were gender-specific: it experienced periodic fluctuations in males and increased approximately two-fold in females
Statistical Mechanics of Torque Induced Denaturation of DNA
A unifying theory of the denaturation transition of DNA, driven by
temperature T or induced by an external mechanical torque Gamma is presented.
Our model couples the hydrogen-bond opening and the untwisting of the
helicoidal molecular structure. We show that denaturation corresponds to a
first-order phase transition from B-DNA to d-DNA phases and that the
coexistence region is naturally parametrized by the degree of supercoiling
sigma. The denaturation free energy, the temperature dependence of the twist
angle, the phase diagram in the T,Gamma plane and isotherms in the sigma, Gamma
plane are calculated and show a good agreement with experimental data.Comment: 5 pages, 3 figures, model improve
Energy funneling in a bent chain of Morse oscillators with long-range coupling
A bent chain of coupled Morse oscillators with long-range dispersive
interaction is considered. Moving localized excitations may be trapped in the
bending region. Thus chain geometry acts like an impurity. An energy funneling
effect is observed in the case of random initial conditions.Comment: 6 pages, 12 figures. Submitted to Physical Review E, Oct. 13, 200
Bubbles, clusters and denaturation in genomic DNA: modeling, parametrization, efficient computation
The paper uses mesoscopic, non-linear lattice dynamics based
(Peyrard-Bishop-Dauxois, PBD) modeling to describe thermal properties of DNA
below and near the denaturation temperature. Computationally efficient notation
is introduced for the relevant statistical mechanics. Computed melting profiles
of long and short heterogeneous sequences are presented, using a recently
introduced reparametrization of the PBD model, and critically discussed. The
statistics of extended open bubbles and bound clusters is formulated and
results are presented for selected examples.Comment: to appear in a special issue of the Journal of Nonlinear Mathematical
Physics (ed. G. Gaeta
On the nonlinear dynamics of topological solitons in DNA
Dynamics of topological solitons describing open states in the DNA double
helix are studied in the frameworks of the model which takes into account
asymmetry of the helix. It is shown that three types of topological solitons
can occur in the DNA double chain. Interaction between the solitons, their
interactions with the chain inhomogeneities and stability of the solitons with
respect to thermal oscillations are investigated.Comment: 16 pages, 16 figure
Bubble propagation in a helicoidal molecular chain
We study the propagation of very large amplitude localized excitations in a
model of DNA that takes explicitly into account the helicoidal structure. These
excitations represent the ``transcription bubble'', where the hydrogen bonds
between complementary bases are disrupted, allowing access to the genetic code.
We propose these kind of excitations in alternative to kinks and breathers. The
model has been introduced by Barbi et al. [Phys. Lett. A 253, 358 (1999)], and
up to now it has been used to study on the one hand low amplitude breather
solutions, and on the other hand the DNA melting transition. We extend the
model to include the case of heterogeneous chains, in order to get closer to a
description of real DNA; in fact, the Morse potential representing the
interaction between complementary bases has two possible depths, one for A-T
and one for G-C base pairs. We first compute the equilibrium configurations of
a chain with a degree of uncoiling, and we find that a static bubble is among
them; then we show, by molecular dynamics simulations, that these bubbles, once
generated, can move along the chain. We find that also in the most unfavourable
case, that of a heterogeneous DNA in the presence of thermal noise, the
excitation can travel for well more 1000 base pairs.Comment: 25 pages, 7 figures. Submitted to Phys. Rev.
A Simple Model for the DNA Denaturation Transition
We study pairs of interacting self-avoiding walks on the 3d simple cubic
lattice. They have a common origin and are allowed to overlap only at the same
monomer position along the chain. The latter overlaps are indeed favored by an
energetic gain.
This is inspired by a model introduced long ago by Poland and Sheraga [J.
Chem. Phys. {\bf 45}, 1464 (1966)] for the denaturation transition in DNA
where, however, self avoidance was not fully taken into account. For both
models, there exists a temperature T_m above which the entropic advantage to
open up overcomes the energy gained by forming tightly bound two-stranded
structures.
Numerical simulations of our model indicate that the transition is of first
order (the energy density is discontinuous), but the analog of the surface
tension vanishes and the scaling laws near the transition point are exactly
those of a second order transition with crossover exponent \phi=1. Numerical
and exact analytic results show that the transition is second order in modified
models where the self-avoidance is partially or completely neglected.Comment: 29 pages, LaTeX, 20 postscript figure
Chronological changes of incidence and prognosis of children with asymptomatic congenital cytomegalovirus infection in Sapporo, Japan
BACKGROUND: Chronological changes of the incidence of congenital cytomegalovirus (CMV) infection and the longitudinal prognosis in children with asymptomatic congenital infection were investigated. METHODS: Congenital CMV infection, as demonstrated by isolation of the virus within the first week of life, was diagnosed in infants born in Sapporo, Japan, during the 26-year period between 1977 and 2002. RESULTS: Congenital infection was diagnosed in 37 (0.31%) of 11,938 infants. Thirty-two infants were (86.5%) asymptomatic and 5 (13.5%) were symptomatic at birth. CONCLUSIONS: Although a decrease in the total incidence of congenital CMV infection has been seen in recent years, screening of congenital infection at birth seems to be necessary to detect late-onset neurodevelopmental sequelae
Measurement of and charged current inclusive cross sections and their ratio with the T2K off-axis near detector
We report a measurement of cross section and the first measurements of the cross section
and their ratio
at (anti-)neutrino energies below 1.5
GeV. We determine the single momentum bin cross section measurements, averaged
over the T2K -flux, for the detector target material (mainly
Carbon, Oxygen, Hydrogen and Copper) with phase space restricted laboratory
frame kinematics of 500 MeV/c. The
results are and $\sigma(\nu)=\left( 2.41\
\pm0.022{\rm{(stat.)}}\pm0.231{\rm (syst.)}\ \right)\times10^{-39}^{2}R\left(\frac{\sigma(\bar{\nu})}{\sigma(\nu)}\right)=
0.373\pm0.012{\rm (stat.)}\pm0.015{\rm (syst.)}$.Comment: 18 pages, 8 figure
Propriedades calorimétricas do biofilme de amido de araruta (Maranta arundinaceae) com diferentes concentrações de nanocelulose de Pinus elliottii.
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