138 research outputs found
Bayesian estimation of Pseudomonas aeruginosa viscoelastic properties based on creep responses of wild type, rugose, and mucoid variant biofilms
No full textPseudomonas aeruginosa biofilms are relevant for a variety of disease settings, including pulmonary infections in people with cystic fibrosis. Biofilms are initiated by individual bacteria that undergo a phenotypic switch and produce an extracellular polymeric slime (EPS). However, the viscoelastic characteristics of biofilms at different stages of formation and the contributions of different EPS constituents have not been fully explored. For this purpose, we develop and parameterize a mathematical model to study the rheological behavior of three biofilms — P. aeruginosa wild type PAO1, isogenic rugose small colony variant (RSCV), and mucoid variant biofilms against a range of experimental data. Using Bayesian inference to estimate these viscoelastic properties, we quantify the rheological characteristics of the biofilm EPS. We employ a Monte Carlo Markov Chain algorithm to estimate these properties of P. aeruginosa variant biofilms in comparison to those of wild type. This information helps us understand the rheological behavior of biofilms at different stages of their development. The mechanical properties of wild type biofilms change significantly over time and are more sensitive to small changes in their composition than the other two mutants
Controller design via structural reduced modeling by FETM
No full textThe Finite Element-Transfer Matrix (FETM) method has been developed to reduce the computations involved in analysis of structures. This widely accepted method, however, has certain limitations, and does not address the issues of control design. To overcome these, a modification of the FETM method has been developed. The new method easily produces reduced models tailored toward subsequent control design. Other features of this method are its ability to: (1) extract open loop frequencies and mode shapes with less computations, (2) overcome limitations of the original FETM method, and (3) simplify the design procedures for output feedback, constrained compensation, and decentralized control. This report presents the development of the new method, generation of reduced models by this method, their properties, and the role of these reduced models in control design. Examples are included to illustrate the methodology
Effects on the Rotation of a Body Containing a Freely Moving Mass Along an Axis
No full textIn this study, a wing system in three different coordinates, x, y and z, was established. The main purpose of this study was to investigate the possibility of increasing rotation of a vehicle in order to escape some dangerous conditions in a short time interval. The angular velocities of masses on the three coordinate axes were examined and the effect of their position on the angular velocity was investigated. The aim was to determine how the angular velocity is increased or decreased and if this occurs immediately by changing the location of the masses. Ultimately, the investigation of changing angular velocity instantaneously to prevent dangerous accidents was targeted by sudden rotation of the vehicle. Initially, the state of the angular velocity was studied when the masses are stationary because the moment of inertia does not play an important role. The result is that the angular velocities for the different masses will be the same value as their initial value. Also, it is assumed that there are no external forces such as gravity and friction. Therefore, our vehicle rotates at the same initial speed. Second, the effect on the angular velocities when some mass on each axis change position and move further down to the outer ends of the system was studied. In this case, 'some mass' means the mass on the axes in which the vehicle is not rotating. In other words, in order to rotate the vehicle about the x-axis, we need to know the positions of the y and z masses. Therefore, there are only two masses that play a role on the vehicle rotation. After setting the initial conditions it was obtained that when the position of the masses was altered, the angular velocities were seen to decrease based on our simulations using the Matlab program. Changing the position of the mass undeniably changes the moment of inertia which in turn cause the angular velocity to change and not stay at the same speed. The last simulation in this study was investigated for the condition when all the masses are not stationary. In this case, all three masses on their respective axes are moving. The respective distances of each mass from its initial starting point and its effect on the angular velocity as the masses moved further towards the outer ends of the system was examined. In the previous case only, movement of two of the three masses were simulated and its effect on angular velocity determined. The critical positioning of the three masses was expected to greatly affect the angular velocity considering that the positions of the mass can significantly alter the angular velocity. The change in positions were simulated in Matlab and it was observed that as the masses moved further outward the angular velocities decrease and reached a constant limit.M.S., Mechanical Engineering and Mechanics -- Drexel University, 201
Global Sensitivity Analysis for the Rothermel Model Based on High Dimensional Model Representation
No full textRothermel’s wildland surface fire spread model is widely used in North America. The model outputs depend on a number of input parameters, which can be broadly categorized as fuel model, fuel moisture, terrain and wind parameters. Due to the inevitable presence of uncertainty in the input parameters, the sensitivity of the model output to a given input parameter can be very useful for understanding and controlling the sources of parametric uncertainty. Instead of obtaining the local sensitivity indices, we perform a global sensitivity analysis that considers the synchronous changes of parameters in their respective ranges. The global sensitivity indices corresponding to different parameter groups are computed by constructing the truncated ANOVA-high dimensional model representation for the model outputs with a polynomial expansion approach. We apply global sensitivity analysis to six standard fuel models, namely, short grass, tall grass, chaparral, hardwood litter, timber and light logging slash. Our sensitivity results show similarities as well as differences between fuel models. For example, the sensitivities of the input parameters fuel depth, low heat content, and wind, are large in all fuel models, and as high as 85% of the total model variance in the fuel model light logging slash. On the other hand, the fuel depth explains around 40% of the total variance in the fuel model light logging slash, but only 12% for the fuel model short grass. The quantification of the importance of parameters across fuel models helps identify the parameters for which additional resources should be used to lower their uncertainty, leading to effective fire management.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
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