Effects of temperature dependent viscosity on Bénard convection in a porous medium using a non-Darcy model

Temperature-dependent viscosity variation effect on Benard convection, of a gas or a liquid, in an enclosure filled with a porous medium is studied numerically, based on the general model of momentum transfer in a porous medium. The exponential form of viscosity-temperature relation is applied to examine three cases of viscosity-temperature relation: constant (mu = mu(C)), decreasing (down to 0.13 mu C) and increasing (up to 7.39 mu(C)). Effects of fluid viscosity variation on isotherms, streamlines, and the Nusselt number are studied. Application of the effective and average Rayleigh number is examined. Defining a reference temperature, which does not change with the Rayleigh number but increases with the Darcy number, is found to be a viable option to account for temperature-dependent viscosity variation. (C) 2007 Published by Elsevier Ltd

Estimating Contact Process Saturation in Sylvatic Transmission of Trypanosoma cruzi in the United States

Although it has been known for nearly a century that strains of Trypanosoma cruzi, the etiological agent for Chagas' disease, are enzootic in the southern U.S., much remains unknown about the dynamics of its transmission in the sylvatic cycles that maintain it, including the relative importance of different transmission routes. Mathematical models can fill in gaps where field and lab data are difficult to collect, but they need as inputs the values of certain key demographic and epidemiological quantities which parametrize the models. In particular, they determine whether saturation occurs in the contact processes that communicate the infection between the two populations. Concentrating on raccoons, opossums, and woodrats as hosts in Texas and the southeastern U.S., and the vectors Triatoma sanguisuga and Triatoma gerstaeckeri, we use an exhaustive literature review to derive estimates for fundamental parameters, and use simple mathematical models to illustrate a method for estimating infection rates indirectly based on prevalence data. Results are used to draw conclusions about saturation and which population density drives each of the two contact-based infection processes (stercorarian/bloodborne and oral). Analysis suggests that the vector feeding process associated with stercorarian transmission to hosts and bloodborne transmission to vectors is limited by the population density of vectors when dealing with woodrats, but by that of hosts when dealing with raccoons and opossums, while the predation of hosts on vectors which drives oral transmission to hosts is limited by the population density of hosts. Confidence in these conclusions is limited by a severe paucity of data underlying associated parameter estimates, but the approaches developed here can also be applied to the study of other vector-borne infections

Modeling the Dynamic Transmission of Dengue Fever: Investigating Disease Persistence

Dengue is the most rapidly spreading mosquito-borne viral disease in the world and approximately 2.5 billion people live in dengue endemic countries. In Brazil it is mainly transmitted by Aedes aegypti mosquitoes. The wide clinical spectrum ranges from asymptomatic infections or mild illness, to the more severe forms of infection such as dengue hemorrhagic fever or dengue shock syndrome. The spread and dramatic increase in the occurrence of dengue cases in tropical and subtropical countries has been blamed on uncontrolled urbanization, population growth and international traveling. Vaccines are under development and the only current disease control strategy is trying to keep the vector quantity at the lowest possible levels. Mathematical models have been developed to help understand the disease's epidemiology. These models aim not only to predict epidemics but also to expand the capacity of phenomena explanation. We developed a spatially explicit model to simulate the dengue transmission in a densely populated area. The model involves the dynamic interactions between humans and mosquitoes and takes into account human mobility as an important factor of disease spread. We investigated the importance of human population size, human renewal rate, household infestation and ratio of vectors per person in the maintenance of sustained viral circulation

Unsteady Double Diffusive Natural Convection in Porous Media-Application to CO2 Storage in Deep Saline Aquifer Reservoirs

AbstractStorage capacity of carbon dioxide (CO2) in deep saline aquifers is a challenging task. However, an assessment must be performed to determine whether there is sufficient capacity in a storage site for any CO2 sequestration project. We evaluated the CO2 storage capacity for a simplified reservoir system, which the layered potential storage formations are overlaid by sealing cap rock.In this paper, we aim to investigate numerically the storage of CO2 at supercritical conditions in deep saline aquifer reservoirs. Numerical simulations were carried out on non-deformable saturated porous material inside a vertical enclosure, assumed to be impermeable and isolated on three sides. The porous medium is considered to be homogeneous and isotropic with constant thermo-physical properties with the exception of the density of the fluid varying according to Boussinesq approximations.A dynamic model assuming that flow is two-dimensional and obeying to Darcy's law for motion has been used. We assume also that the thermal equilibrium assumption is valid. The set of the conservation equations along with the appropriate initial and boundary conditions have been resolved numerically by the classical finite volume method [1]. Spatio-temporal variations of different state variables such as pressure, velocity, temperature and concentration were numerically simulated and plotted versus different controlling parameters particularly, thermal and solutal Rayleigh numbers and Lewis number. Great attention was paid to examine the sensitivity of heat and mass transfer rates according to the reservoir form and the operating conditions

Zuverlässige Ad-Hoc Kommunikation mobiler Endgeräte mit satellitengestützter Internet-Anbindung

Mobile Datenkommunikation basiert üblicherweise auf der drahtlosen Anbindung eines Endgerätes an eine Basisstation, die ihrerseits an eine feste Infrastruktur angebunden ist. In vielen Szenarien sind diese Voraussetzungen jedoch nicht gegeben. Beispiele hierfür sind Hochwasser, Erdbeben oder Flugzeugabstürze in dünn besiedelten Regionen. Einen Lösungsansatz für sich daraus ergebende Anforderungen bieten dynamisch aufgebaute Ad-Hoc Netze mit einer satellitengestützten Anbindung an eine Festnetz-Infrastruktur. In solchen Netzen stellen die mobilen Terminals die benötigte lokale Infrastruktur selbst dynamisch her. Ziel der hier vorgestellten Arbeiten ist es, die Zuverlässigkeit und Dienstqualität der verwendeten Technologien zu untersuchen und durch geeignete Mechanismen so anzupassen, dass die Anforderungen typischer Applikationen möglichst erfüllt werden. Zur Demonstration wurde ein Prototyp aufgebaut, der unter anderem die Anwendungen "Voice over IP" (VoIP), "Datenbankzugriff im Intranet" und Internetzugang (WWW) untersucht