Mathematical Biology Seminar

Seminar information archive ~04/12Next seminarFuture seminars 04/13~


Seminar information archive

2014/06/11

14:50-16:20   Room #128 (Graduate School of Math. Sci. Bldg.)
Tetsuya Kobayashi (Center for Research on Integrated Biomedical Systems, Institute of Industrial Science, the University of Tokyo
)
Path Integral Formulation and Variational Structure in Multitype Population Dynamics
(JAPANESE)

2014/05/28

14:50-16:20   Room #128 (Graduate School of Math. Sci. Bldg.)
Keisuke Ejima (Department of Global Health Policy, Graduate School of Medicine, The University of Tokyo
)
Modeling the social contagion: The obesity epidemic and its control (JAPANESE)
[ Abstract ]
:As an obesity epidemic has grown worldwide, a variety of
intervention programs have been considered, but a scientific approach
to comparatively assessing the control programs has still to be
considered. The present study aims to describe an obesity epidemic by
employing a simple mathematical model that accounts for both social
contagion and non-contagious hazards of obesity, thereby comparing the
effectiveness of different types of interventions.
An epidemiological model is devised to describe the time- and
age-dependent risk of obesity, the hazard of which is dealt with as
both dependent on and independent of obesity prevalence, and
parameterizing the model using empirically observed data. The
equilibrium prevalence is investigated as our epidemiological outcome,
assessing its sensitivity to different parameters that regulate the
impact of intervention programs and qualitatively comparing the
effectiveness. We compare the effectiveness of different types of
interventions, including those directed to never-obese individuals
(i.e. primary prevention) and toward obese and ex-obese individuals
(i.e. secondary prevention).
The optimal choice of intervention programs considerably varies with
the transmission coefficient of obesity, and a limited
transmissibility led us to favour preventing weight gain among
never-obese individuals. An abrupt decline in the prevalence is
expected when the hazards of obesity through contagious and
non-contagious routes fall into a particular parameter space, with a
high sensitivity to the transmission potential of obesity from person
to person. When a combination of two control strategies can be
selected, primary and secondary preventions yielded similar population
impacts and the superiority of the effectiveness depends on the
strength of the interventions at an individual level.
The optimality of intervention programs depends on the contagiousness
of obesity. Filling associated data gaps of obesity transmission would
help systematically understand the epidemiological dynamics and
consider required control programs.

2014/05/07

14:50-16:20   Room #128 (Graduate School of Math. Sci. Bldg.)
Yoichi Enatsu (Graduate School of Mathematical Sciences, University fo Tokyo)
Asymptotic behavior of differential equation systems for age-structured epidemic models (JAPANESE)

2014/04/23

14:50-16:20   Room #128 (Graduate School of Math. Sci. Bldg.)
Yukihiko Nakata (Graduate School of Mathematical Sciences, University of Tokyo)
Age-structured epidemic model with infection during transportation (JAPANESE)

2014/03/12

15:00-17:00   Room #126 (Graduate School of Math. Sci. Bldg.)
Andre M. de Roos (University of Amsterdam)
When size does matter: Ontogenetic symmetry and asymmetry in energetics
(ENGLISH)
[ Abstract ]
Body size (≡ biomass) is the dominant determinant of population dynamical processes such as giving birth or dying in almost all species, with often drastically different behaviour occurring in different parts of the growth trajectory, while the latter is largely determined by food availability at the different life stages. This leads to the question under what conditions unstructured population models, formulated in terms of total population biomass, still do a fair job. To contribute to answering this question we first analyze the conditions under which a size-structured model collapses to a dynamically equivalent unstructured one in terms of total biomass. The only biologically meaningful case where this occurs is when body size does not affect any of the population dynamic processes, this is the case if and only if the mass-specific ingestion rate, the mass-specific biomass production and the mortality rate of the individuals are independent of size, a condition to which we refer as “ontogenetic symmetry”. Intriguingly, under ontogenetic symmetry the equilibrium biomass-body size spectrum is proportional to 1/size, a form that has been conjectured for marine size spectra and subsequently has been used as prior assumption in theoretical papers dealing with the latter. As a next step we consider an archetypical class of models in which reproduction takes over from growth upon reaching an adult body size, in order to determine how quickly discrepancies from ontogenetic symmetry lead to relevant novel population dynamical phenomena. The phenomena considered are biomass overcompensation, when additional imposed mortality leads, rather unexpectedly, to an increase in the equilibrium biomass of either the juveniles or the adults (a phenomenon with potentially big consequences for predators of the species), and the occurrence of two types of size-structure driven oscillations, juvenile-driven cycles with separated extended cohorts, and adult-driven cycles in which periodically a front of relatively steeply decreasing frequencies moves up the size distribution. A small discrepancy from symmetry can already lead to biomass overcompensation; size-structure driven cycles only occur for somewhat larger discrepancies.
[ Reference URL ]
http://staff.science.uva.nl/~aroos/

2013/07/29

16:30-18:00   Room #118 (Graduate School of Math. Sci. Bldg.)
Yoichi Enatsu (Graduate School of Mathematical Sciences, University of Tokyo)
Characteristic changes by time delay in the solution of differential equation and their applications (JAPANESE)

2013/07/18

16:30-18:00   Room #118 (Graduate School of Math. Sci. Bldg.)
Ryo Oizumi (Graduate School of Environmental Science, Hokkaido University)
Path integral representaion and Euler-Lotka equation in age-size structured population model (JAPANESE)

2013/01/15

14:00-16:00   Room #152 (Graduate School of Math. Sci. Bldg.)
Yukihiko Nakata (
Bolyai Institute, University of Szeged)
Differential equation models describing cell proliferation process and their dynamics (JAPANESE)

2013/01/15

14:00-16:00   Room #152 (Graduate School of Math. Sci. Bldg.)
Shinji Nakaoka (RIKEN)
Formulation of transient amplifying cell population growth process based on generation progression models (JAPANESE)

2012/11/30

14:30-15:30   Room #056 (Graduate School of Math. Sci. Bldg.)
Michael Tildesley ( Infectious Disease Epidemiology (Modelling) at the University of Warwick)
Targeting control in the presence of uncertainty (ENGLISH)
[ Abstract ]
The availability of epidemiological data in the early stages of an outbreak of an infectious disease is vital to enable modellers to make accurate predictions regarding the likely spread of disease and preferred intervention strategies. However, in some countries, epidemic data are not available whilst necessary demographic data are only available at an aggregate scale. Here we investigate the ability of models of livestock infectious diseases to predict epidemic spread and optimal control policies in the event of uncertainty. We focus on investigating predictions in the presence of uncertainty regarding contact networks, demographic data and epidemiological parameters. Our results indicate that mathematical models could be utilized in regions where individual farm-level data are not available, to allow predictive analyses to be carried out regarding the likely spread of disease. This method can also be used for contingency planning in collaboration with policy makers to determine preferred control strategies in the event of a future outbreak of infectious disease in livestock.

2012/03/13

14:00-15:00   Room #154 (Graduate School of Math. Sci. Bldg.)
Tsuyoshi Kajiwara (Okayama University)
On construction of Lyapunov functions and functionals (JAPANESE)

2010/04/19

16:30-18:00   Room #056 (Graduate School of Math. Sci. Bldg.)
Horoshi HAENO (Memorial Sloan-Kettering Cancer Center)
骨髄増殖性疾患の起源細胞に関する数理的研究 (JAPANESE)

2010/01/20

14:40-16:10   Room #052 (Graduate School of Math. Sci. Bldg.)
江島啓介 (東京大学情報理工学研究科数理情報専攻修士課程)
東京都市圏パーソントリップ調査に基づく新型インフルエンザ感染拡大シミュレーション
[ Abstract ]
新型インフルエンザの感染拡大に対する対応策として,学校施設等の閉鎖など外
出時の感染機会を減らすための措置が考えられるが,その効果は十分に明らかで
はない.そこで本研究では,individual based modelに東京都市圏パーソント
リップ調査を組み合わせることにより感染拡大モデルを構築し,数値シミュレー
ションによって外出規制および施設閉鎖の効果を検討した.外出規制に関して
は,規制日数が12日以上と長い場合には効果が大きいことがわかった.また,施
設閉鎖に関しては,閉鎖期間・閉鎖基準を厳しくすると,ピークまでの日数は変
わらないものの,累積罹患率は低下することがわかった.

2009/12/24

16:00-17:30   Room #123 (Graduate School of Math. Sci. Bldg.)
堀内 四郎 (The City University of New York, Hunter College)
Decomposition分析:趨勢データ分析の新しい枠組とアプローチ
[ Abstract ]
A demographic measure is often expressed as a deterministic or stochastic function of multiple variables (covariates), and a general problem (the decomposition problem) is to assess contributions of individual covariates to a difference in the demographic measure (dependent variable) between two populations.

We propose a method of decomposition analysis based on an assumption that covariates change continuously along an actual or hypothetical dimension. This assumption leads to a general model that logically justifi es the additivity of covariate effects and the elimination of interaction terms, even if the dependent variable itself is a nonadditive function.

A comparison with earlier methods illustrates other practical advantages of the method: in addition to an absence of residuals or interaction terms, the method can easily handle a large number of covariates and does not require a logically meaningful ordering of covariates. Two empirical examples show that the method can be applied fl exibly to a wide variety of decomposition problems.
[ Reference URL ]
http://shiro_horiuchi.homestead.com/homepage.html

2009/07/16

15:00-16:20   Room #056 (Graduate School of Math. Sci. Bldg.)
Odo Diekmann (Mathematical Institute, Utrecht University)
The delay equation formulation of physiologically structured population models
[ Abstract ]
Traditionally, physiologically structured population models are formulated in terms of first order partial differential equations with non-local boundary conditions and/or transformed arguments. The stability and bifurcation theory for such equations is, in the quasi-linear case, still very immature.
The aim of this lecture is to explain that, alternatively, one can formulate such models in terms of delay equations (more precisely : renewal equations coupled to delay differential equations) without losing essential information and that for delay equations there is a well-developed local stability and bifurcation theory. As a motivating example we consider the interaction between a size-structured consumer and an unstructured resource. The lecture is based on joint work with Mats Gyllenberg and Hans Metz.

2009/05/14

16:00-17:30   Room #123 (Graduate School of Math. Sci. Bldg.)
岩見真吾 (静岡大学創造科学技術大学院)
AIDSワクチン開発への理論的介入-SHIV感染実験と数理モデル-
[ Abstract ]
慢性感染症であるという特性を有するHIV感染症の拡大を阻止するためには、予防・治療AIDSワクチンの開発が不可欠である。しかし、1998年にヒトでは初めての国際的な臨床試験が始まったバックスジェン社のAIDSワクチンは、2003年に失敗だと発表された。また、2004年メルク社の最も有望だったワクチン候補も大規模な臨床試験にまで進んだが、効果がないどころか悪影響がある可能性が判明し、2007年に打ち切られた。HIV単離からすでに25年たった今でも、まだ効果的なワクチンは開発されていない。このように、HIVに対して従来のワクチン製造法では有効なワクチンを作れなかったとなれば、何かこれまでとは違う革新的な治療戦略が必要である。そこで、本研究では、HIVとその体内での振る舞いに関する基本的な疑問と取り組み、HIVを無力化する新しい方法を見つけ出すこと目指す。まず身体に備わった免疫応答が通常どのように機能するのかを知るために、HIVとよく似たSHIVの感染実験と数理モデルを用いて、SHIVの性状、病原性、免疫反応性を明らかにする。今回のセミナーでは、培養細胞での実験データから推定可能であるウイルスの増殖率と感染力によって特徴づけられるSHIVの病原性評価理論を紹介する。

2008/06/09

16:30-17:30   Room #126 (Graduate School of Math. Sci. Bldg.)
中岡 慎治 (東京大学大学院数理科学研究科)
幼生の行動変化が個体群動態に及ぼす影響の数理モデル
[ Abstract ]
動物の行動変化は個体群動態に影響を及ぼし得る。群生はもっとも良く知られた
動物行動の一つで、凝集することによって捕食者から狙われるリスクを回避する
ような効果(たとえば希釈効果)などがある。、たとえば幼生は成体に比べて一般に
捕食に会うリスクが高いため、個体の成長は行動を決める上で非常に重要な要因
である。
本研究では捕食者にステージ構造を考慮した捕食者被食者数理モデルを
構築し、動物の行動変化が個体群動態に及ぼす影響を調べた。もし種内で資源を
めぐる競争が激しい場合、上位の捕食者による捕食リスクが増えるにつれて
凝集して群生することは必ずしもメリットとはならず、Allee 効果による突然の
群生消滅が生じる可能性があることを数理モデルの解析・シミュレーションに
よって明らかにした。

2007/06/13

14:40-15:40   Room #123 (Graduate School of Math. Sci. Bldg.)
Alex Cook (Actuarial Mathematics and Statistics,
School of Mathematical and Computer Sciences,
Heriot-Watt University)
Return of the Giant Hogweed: modelling the invasion of Britain by a dangerous alien plant
[ Abstract ]
As a result of changing climate and land use, as well as due to human intervention, increasingly species are moving to new abitats. We wish to understand the risk of invasive species entering new areas, and as an example consider the spread of Giant Hogweed (Heracleum mantegazzianum) from SW Asia in Great Britain, a species that has been damaging Britain's biodiversity since it was introduced in the 19th C and which is dangerous to human health. We construct a spatio-temporal stochastic model for its spread (both local and at distance) that takes account of covariates such as the heterogeneous land-cover and climate of the island. We then fit the model directly to observed data. Fitting the model was non-trivial and involved the use of Markov chain Monte Carlo techniques. The approach taken allows spatio-temporal predictions of the future spread of the weed can be made, consistent with the invasion history; it also allows the effect of varying habitats and climate to be understood. The approach we have taken can be generalised to other biological systems exhibiting stochastic variability, and there are clear parallels to epidemic models for the spread of disease within heterogeneous host populations.
[ Reference URL ]
http://www.ma.hw.ac.uk/~alexc/

2006/10/06

16:30-17:30   Room #123 (Graduate School of Math. Sci. Bldg.)
石井 太 (国立社会保障・人口問題研究所)
人口指標の精度について
[ Abstract ]
近年の急速な少子化の進行に伴い、出生率の動向への関心が高まっている。しかしながら、その指標が注目され、様々に論じられる中に、指標の持つ精度を度外視した議論なども見受けられる。人口統計は人口分析の中心となるデータソースであり、人口指標の精度は重要な問題であるが、わが国においてはこれまで比較的精度の高い人口統計が取得されてきたこともあり、それほど重視せず、確定的なものと捉えがちな傾向があったように思われる。一方では、近年、統計調査環境の悪化などもあり、各々の人口指標についてどこまで詳細な議論が可能なのか、指標の精度について理論的・実務的な観点からより深い認識を持つことが必要となってきている。
本報告では、出生率での具体例を中心に、さまざまな誤差の発生要因に応じた人口指標の評価について提示することとしたい。

2006/09/27

16:30-17:30   Room #123 (Graduate School of Math. Sci. Bldg.)
中丸麻由子 (東京工業大学)
The coevolution of altruism and punishment:role of the selfish punisher
[ Abstract ]
Punishment is an important mechanism promoting the evolution of altruism among nonrelatives. We investigate the coevolution of altruism and punitive behavior, considering four strategies: a cooperator who punishes defectors (AP), a pure cooperator (AN), a defector who punishes defectors (selfish punisher or SP), and a pure defector (SN). We especially focus on the effects of SP on the coevolution of altruism and punishment, studying both the score-dependent viability model (whereby the game's score affects survivorship only) and the score-dependent fertility model (whereby the score affects fertility only). In the viability model of a completely mixed population, SP helps cooperators to evolve, but SP does not in the fertility model. In both models of a lattice-structured population, SP promotes the spread of AP, but AN discourages it. These results indicate that punishment is a form of spite behavior and that different models give different magnitude of advantage to spite behavior.

2006/05/29

16:00-17:00   Room #056 (Graduate School of Math. Sci. Bldg.)
池 周一郎 (帝京大学文学部社会学科)
拡散モデルによる夫婦の子ども数の低下

< Previous 123