Global stability for epidemic model with constant latency and infectious periods.

In recent years many delay epidemiological models have been proposed to study at which stage of the epidemics the delays can destabilize the disease free equilibrium, or the endemic equilibrium, giving rise to stability switches. One of these models is the SEIR model with constant latency time and infectious periods [2], for which the authors have proved that the two delays are harmless in inducing stability switches. However, it is left open the problem of the global asymptotic stability of the endemic equilibrium whenever it exists. Even the Lyapunov functions approach, recently proposed by Huang and Takeuchi to study many delay epidemiological models, fails to work on this model. In this paper, an age-infection model is presented for the delay SEIR epidemic model, such that the properties of global asymptotic stability of the equilibria of the age-infection model imply the same properties for the original delay-differential epidemic model. By introducing suitable Lyapunov functions to study the global stability of the disease free equilibrium (when $\mathcal{R}_0\leq 1$) and of the endemic equilibria (whenever $\mathcal{R}_0>1$) of the age-infection model, we can infer the corresponding global properties for the equilibria of the delay SEIR model in [2], thus proving that the endemic equilibrium in [2] is globally asymptotically stable whenever it exists. &nbsp Furthermore, we also present a review of the SIR, SEIR epidemic models, with and without delays, appeared in literature, that can be seen as particular cases of the approach presented in the paper

Special Issue "Lentiviral Vectors"

Lentiviral vectors (LV) have been developed upon knowledge accumulated in the virology field, in particular intensive research on HIV biology since its discovery in 1983 [...]

Discussion of Possible Semantic Description for Documents Based on Analysis of Predicate-Argument Structure

動詞間で共通する意味属性を考慮して,シソーラス上に整理した動詞項構造シソーラスを提案し,形容動詞まで拡張して分析を進めてきた.動詞項構造シソーラスの背景には語彙概念構造という状態変化を主に記述する形式を拡張してきたが,「必要だ」や「必ず〜する」といった主観的な内容を記述する場所が無く,意味記述の中に自然言語で埋めることになっている.本稿では述語の分析から必要となる意味構造の要件を明らかにする.その中でも可能世界意味論に関係している点を事例をもとに明確化し,文書解析のための意味構造について考察する.さらに,人工知能で議論されてきた様相論理,動的命題,設計学,オントロジー工学との関係について概観する.The results of our previous work of construction of Japanese verb thesaurus revealed that a verb meaning often contains not only action or change-of-state meaning, i.e., objective meaning, but subjective meanings. To describe verb meaning, lexical conceptual structure was applied, but it does not have a place of subjective and modal meaning; then they are described using natural language embedded in an extended LCS-based schema. Modal logic gives us a description framework, but verb meanings have more complex meaning, such as event attributes, progress and possibility. In the manuscript we summarize the wide variety of verb and adjective verb meaning from the view of change-of-state and subjective meaning, then discuss a description framework of them according to modal logic study

Permanence of a single-species dispersal system and predator survival

AbstractThis paper considers permanence of a single-species dispersal periodic system with the possibility of the loss for the species during their dispersion among patches. The condition obtained for permanence generalizes the known condition on the system without loss for the species in the process of movement. Next, we add predators into every patch and consider the survival possibility of the predator. It is shown that the total amount of the predators can remain positive, if the single-species (prey) dispersal system has a positive periodic solution and the quantity of prey in each patch is enough for survival of the predator