Dynamics of a structured slug population model in the absence of seasonal variation

We develop a novel, nonlinear structured population model for the slug Deroceras reticulatum, a highly significant agricultural pest of great economic impact, in both organic and non-organic settings. In the absence of seasonal variations, we numerically explore the effect of life history traits that are dependent on an individual's size and measures of population biomass. We conduct a systematic exploration of parameter space and highlight the main mechanisms and implications of model design. A major conclusion of this work is that strong size dependent predation significantly adjusts the competitive balance, leading to non-monotonic steady state solutions and slowly decaying transients consisting of distinct generational cycles. Furthermore, we demonstrate how a simple ratio of adult to juvenile biomass can act as a useful diagnostic to distinguish between predated and non-predated environments, and may be useful in agricultural settings

Endovascular Stent Grafts as a Safe Secondary Option for Paraanastomotic Abdominal Aortic Aneurysm

ObjectiveTo describe our experience of endovascular repair of paraanastomotic aortic aneurysm.Methods and resultsFrom March 2001 to December 2004 we identified 6 patients with a paraanastomotic aortic aneurysms following previous open repair of abdominal aortic aneurysm. All patients were treated with endovascular surgery under epidural anaesthesia. There were no major complications, surgical conversions or deaths. Four patients received a bifurcated aortic stent-graft, and two an aorto-uniliac stent-graft followed by a femoro-femoral bypass. At follow-up (mean 26.1±10.2 months) there were no deaths, endoleaks or graft migrations observed.ConclusionEndovascular surgery, avoiding general anesthesia and re-laparotomy, is the ideal technique for treatment of this complication resulting from failed primary conventional AAA repair

Endovascular Stent Grafts as a Safe Secondary Option for Paraanastomotic Abdominal Aortic Aneurysm

Objective: To describe our experience of endovascular repair of paraanastomotic aortic aneurysm. Methods and results: From March 2001 to December 2004 we identified 6 patients with a paraanastomotic aortic aneurysms following previous open repair of abdominal aortic aneurysm. All patients were treated with endovascular surgery under epidural anaesthesia. There were no major complications, surgical conversions or deaths. Four patients received a bifurcated aortic stent-graft, and two an aorto-uniliac stent-graft followed by a femoro-femoral bypass. At follow-up (mean 26.1 ± 10.2 months) there were no deaths, endoleaks or graft migrations observed. Conclusion: Endovascular surgery, avoiding general anesthesia and re-laparotomy, is the ideal technique for treatment of this complication resulting from failed primary conventional AAA repair. © 2006 Elsevier Ltd. All rights reserved

Kinetic theory of age-structured stochastic birth-death processes

Classical age-structured mass-action models such as the McKendrick-von Foerster equation have been extensively studied but are unable to describe stochastic fluctuations or population-size-dependent birth and death rates. Stochastic theories that treat semi-Markov age-dependent processes using, e.g., the Bellman-Harris equation do not resolve a population's age structure and are unable to quantify population-size dependencies. Conversely, current theories that include size-dependent population dynamics (e.g., mathematical models that include carrying capacity such as the logistic equation) cannot be easily extended to take into account age-dependent birth and death rates. In this paper, we present a systematic derivation of a new, fully stochastic kinetic theory for interacting age-structured populations. By defining multiparticle probability density functions, we derive a hierarchy of kinetic equations for the stochastic evolution of an aging population undergoing birth and death. We show that the fully stochastic age-dependent birth-death process precludes factorization of the corresponding probability densities, which then must be solved by using a Bogoliubov-–Born–-Green–-Kirkwood-–Yvon-like hierarchy. Explicit solutions are derived in three limits: no birth, no death, and steady state. These are then compared with their corresponding mean-field results. Our results generalize both deterministic models and existing master equation approaches by providing an intuitive and efficient way to simultaneously model age- and population-dependent stochastic dynamics applicable to the study of demography, stem cell dynamics, and disease evolution