243 research outputs found
Size-structured populations: immigration, (bi)stability and the net growth rate
We consider a class of physiologically structured population models, a first
order nonlinear partial differential equation equipped with a nonlocal boundary
condition, with a constant external inflow of individuals. We prove that the
linearised system is governed by a quasicontraction semigroup. We also
establish that linear stability of equilibrium solutions is governed by a
generalized net reproduction function. In a special case of the model
ingredients we discuss the nonlinear dynamics of the system when the spectral
bound of the linearised operator equals zero, i.e. when linearisation does not
decide stability. This allows us to demonstrate, through a concrete example,
how immigration might be beneficial to the population. In particular, we show
that from a nonlinearly unstable positive equilibrium a linearly stable and
unstable pair of equilibria bifurcates. In fact, the linearised system exhibits
bistability, for a certain range of values of the external inflow, induced
potentially by All\'{e}e-effect.Comment: to appear in Journal of Applied Mathematics and Computin
Structured and unstructured continuous models for Wolbachia infections
We introduce and investigate a series of models for an infection of a diplodiploid host species by the bacterial endosymbiont Wolbachia. The continuous models are characterized by partial vertical transmission, cytoplasmic incompatibility and fitness costs associated with the infection. A particular aspect of interest is competitions between mutually incompatible strains. We further introduce an age-structured model that takes into account different fertility and mortality rates at different stages of the life cycle of the individuals. With only a few parameters, the ordinary differential equation models exhibit already interesting dynamics and can be used to predict criteria under which a strain of bacteria is able to invade a population. Interestingly, but not surprisingly, the age-structured model shows significant differences concerning the existence and stability of equilibrium solutions compared to the unstructured model
Flavor Decomposition of the Polarized Quark Distributions in the Nucleon from Inclusive and Semi-inclusive Deep-inelastic Scattering
Spin asymmetries of semi-inclusive cross sections for the production of
positively and negatively charged hadrons have been measured in deep-inelastic
scattering of polarized positrons on polarized hydrogen and 3He targets, in the
kinematic range 0.023<x<0.6 and 1 GeV^2<Q^2<10 GeV^2. Polarized quark
distributions are extracted as a function of x for up $(u+u_bar) and down
(d+d_bar) flavors. The up quark polarization is positive and the down quark
polarization is negative in the measured range. The polarization of the sea is
compatible with zero. The first moments of the polarized quark distributions
are presented. The isospin non-singlet combination Delta_q_3 is consistent with
the prediction based on the Bjorken sum rule. The moments of the polarized
quark distributions are compared to predictions based on SU(3)_f flavor
symmetry and to a prediction from lattice QCD.Comment: 14 pages, 6 figures (eps format), 10 tables in Latex New version
contains tables of asymmetries and correlation matri
Stress testing and non-invasive coronary angiography in patients with suspected coronary artery disease: time for a new paradigm
Diagnosis and management of coronary artery disease represents major challenges to our health care system, affecting millions of patients each year. Until recently, the diagnosis of coronary artery disease was possible only through cardiac catheterization and invasive coronary angiography. To avoid the risks of an invasive procedure, stress testing is often employed for an initial assessment of patients with suspected coronary artery disease, serving as a gatekeeper for cardiac catheterization. With the emergence of non-invasive coronary angiography, the question arises if such a strategy is still sensible, particularly, in view of only a modest agreement between stress testing results and the presence of coronary artery disease established by cardiac catheterization. Much data in support of the diagnostic accuracy and prognostic value of non-invasive coronary angiography by computed tomography have emerged within the last few years. These data challenge the role of stress testing as the initial imaging modality in patients with suspected coronary artery disease. This article reviews the clinical utility, limitations, as well as the hazards of stress testing compared with non-invasive coronary artery imaging by computed tomography. Finally, the implications of this review are discussed in relation to clinical practice
A compendium of multi-omics data illuminating host responses to lethal human virus infections
Human infections caused by viral pathogens trigger a complex gamut of host responses that limit disease, resolve infection, generate immunity, and contribute to severe disease or death. Here, we present experimental methods and multi-omics data capture approaches representing the global host response to infection generated from 45 individual experiments involving human viruses from the Orthomyxoviridae, Filoviridae, Flaviviridae, and Coronaviridae families. Analogous experimental designs were implemented across human or mouse host model systems, longitudinal samples were collected over defined time courses, and global multi-omics data (transcriptomics, proteomics, metabolomics, and lipidomics) were acquired by microarray, RNA sequencing, or mass spectrometry analyses. For comparison, we have included transcriptomics datasets from cells treated with type I and type II human interferon. Raw multi-omics data and metadata were deposited in public repositories, and we provide a central location linking the raw data with experimental metadata and ready-to-use, quality-controlled, statistically processed multi-omics datasets not previously available in any public repository. This compendium of infection-induced host response data for reuse will be useful for those endeavouring to understand viral disease pathophysiology and network biology
Dense Stellar Populations: Initial Conditions
This chapter is based on four lectures given at the Cambridge N-body school
"Cambody". The material covered includes the IMF, the 6D structure of dense
clusters, residual gas expulsion and the initial binary population. It is aimed
at those needing to initialise stellar populations for a variety of purposes
(N-body experiments, stellar population synthesis).Comment: 85 pages. To appear in The Cambridge N-body Lectures, Sverre Aarseth,
Christopher Tout, Rosemary Mardling (eds), Lecture Notes in Physics Series,
Springer Verla
Erratum to: "Nuclear Effects on R=\sigma_L/\sigma_T in Deep-Inelastic Scattering" Phys.Lett. B475(2000)386
This erratum revokes the main conclusion of a Letter that reported
measurements of cross sections for deep-inelastic scattering (DIS) of leptons
on He and N targets, expressed as ratios of to
the cross section on the deuterium target.Comment: 3 pages, 1 figur
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