25 research outputs found
Applications of Center Manifolds
No full textCenter manifolds play a crucial role in the analysis of meta-stable behaviour in dynamical systems, but they are often omitted from undergraduate treatments due to the technical nature of their computation. We overcome this difficulty with symbolic manipulation and present several specific dynamical systems in dimensions two and three in which center manifolds can be employed in an undergraduate setting to emphasise the role played by linearization, provide a natural introduction to normal forms, and resolve interesting cases of balanced forces and meta-stable dynamics. Introduction Junior-Senior level courses in dynamical systems have enjoyed tremendous recent growth in popularity. Partial evidence of this is the explosion in number of texts devoted to the subject. This article presents the author's experience teaching a course "Dynamics and Bifurcations " at Simon Fraser University using the text "Nonlinear Dynamics and Chaos" by Steven Strogatz [3]. The course covered the fundamen..
Trypanosomatids are common and diverse parasites of Drosophila
No full textDrosophila melanogaster is an important model system of immunity and parasite resistance, yet most studies use parasites that do not naturally infect this organism. We have studied trypanosomatids in natural populations to assess the prevalence and diversity of these gut parasites. We collected several species of Drosophila from Europe and surveyed them for trypanosomatids using conserved primers for two genes. We have used the conserved GAPDH sequence to construct a phylogenetic tree and the highly variable spliced leader RNA to assay genetic diversity. All 5 of the species that we examined were infected, and the average prevalence ranged from 1 to 6%. There are several different groups of trypanosomatids, related to other monoxenous Trypanosomatidae. These may represent new trypanosomatid species and were found in different species of European Drosophila from different geographical locations. The detection of a little studied natural pathogen in D. melanogaster and related species provides new opportunities for research into both the Drosophila immune response and the evolution of hosts and parasites.</p
How Well Does the Internet Answer Patients’ Questions about Inflammatory Bowel Disease?
No full textBACKGROUND: The Internet is an increasingly important source of health information
Life is Cheap: Using Mortality Bonds to Hedge Aggregate Mortality Risk
No full textUsing the widely-cited Lee-Carter mortality model, we quantify aggregate mortality risk as the risk that the average annuitant lives longer than is predicted by the model, and we conclude that annuity business exposes insurance companies to substantial mortality risk. We calculate that a markup of 3.7% on an annuity premium (or else shareholders%u2019 capital equal to 3.7% of the expected present value of annuity payments) would reduce the probability of insolvency resulting from uncertain aggregate mortality trends to 5% and a markup of 5.4% would reduce the probability of insolvency to 1%. Using the same model, we find that a projection scale commonly referred to by the insurance industry underestimates aggregate mortality improvements. Annuities that are priced on that projection scale without any conservative margin appear to be substantially underpriced. Insurance companies could deal with aggregate mortality risk by transferring it to financial markets through mortality-contingent bonds, one of which has recently been offered. We calculate the returns that investors would have obtained on such bonds had they been available over a long period. Using both the Capital and the Consumption Capital Asset Pricing Models, we determine the risk premium that investors would have required on such bonds. At plausible coefficients of risk aversion, annuity providers should be able to hedge aggregate mortality risk via such bonds at a very low cost.
Meta-analyses identify 13 loci associated with age at menopause and highlight DNA repair and immune pathways
No full textTo newly identify loci for age at natural menopause, we carried out a meta-analysis of 22 genome-wide association studies (GWAS) in 38,968 women of European descent, with replication in up to 14,435 women. In addition to four known loci, we identified 13 loci newly associated with age at natural menopause (at P < 5 × 10(-8)). Candidate genes located at these newly associated loci include genes implicated in DNA repair (EXO1, HELQ, UIMC1, FAM175A, FANCI, TLK1, POLG and PRIM1) and immune function (IL11, NLRP11 and PRRC2A (also known as BAT2)). Gene-set enrichment pathway analyses using the full GWAS data set identified exoDNase, NF-κB signaling and mitochondrial dysfunction as biological processes related to timing of menopause
Pulmonary arterial hypertension associated with abatacept treatment for rheumatoid arthritis: A case report
No full textBenchmark Computation of Morphological Complexity in the Functionalized Cahn-Hilliard Gradient Flow
No full textReductions of the self-consistent mean field theory model of amphiphilic
molecules in solvent can lead to a singular family of functionalized
Cahn-Hilliard energies. We modify these energies, mollifying the singularities
to stabilize the computation of the gradient flows and develop a series of
benchmark problems that emulate the "morphological complexity" observed in
experiments. These benchmarks investigate the delicate balance between the rate
of absorption of amphiphilic material onto an interface and a least energy
mechanism to disperse the arriving mass. The result is a trichotomy of
responses in which two-dimensional interfaces either lengthen by a regularized
motion against curvature, undergo pearling bifurcations, or split directly into
networks of interfaces. We evaluate a number of schemes that use second order
BDF2-type time stepping coupled with Fourier pseudo-spectral spatial
discretization. The BDF2-type schemes are either based on a fully implicit time
discretization with a PSD nonlinear solver, or upon IMEX, SAV, ETD approaches.
All schemes use a fixed local truncation error target with adaptive
time-stepping to achieve the error target. Each scheme requires proper
"preconditioning" to achieve robust performance that can enhance efficiency by
several orders of magnitude.Comment: 39 pages,18 figures,7 table
Happiness and sex difference in life expectancy
No full textThis paper examines the effects of happiness on the sex gap in life expectancy. Utilizing a cross-country data set, it first inspects the reverse effect of the life expectancy gap on happiness and demonstrates that the life expectancy gap negatively affects happiness through the composition of marital status. Taking this reverse causality into account, it shows that happiness is significant on explaining the differences in the life expectancy gap between countries. As national average happiness increases, the sex difference in life expectancy decreases. This is consistent with the findings that psychological stress (unhappiness)adversely affects survival and that the effect of psychological stress on mortality is more severe for men. This result provides an indirect evidence that happiness affects survival even at the national aggregate level.economic and social development, life expectancy
The effects of graded levels of calorie restriction XV : phase space attractors reveal distinct behavioral phenotypes
No full text© The Author(s) 2020. Published by Oxford University Press on behalf of The Gerontological Society of America. All rights reserved. For permissions, please e-mail: [email protected] reviewe
