Drip and Mate Operations Acting in Test Tube Systems and Tissue-like P systems

The operations drip and mate considered in (mem)brane computing resemble the operations cut and recombination well known from DNA computing. We here consider sets of vesicles with multisets of objects on their outside membrane interacting by drip and mate in two different setups: in test tube systems, the vesicles may pass from one tube to another one provided they fulfill specific constraints; in tissue-like P systems, the vesicles are immediately passed to specified cells after having undergone a drip or mate operation. In both variants, computational completeness can be obtained, yet with different constraints for the drip and mate operations

MOLECULAR COMPUTING WITH TEST TUBE SYSTEMS

In this paper a survey of various different theoretical models of test tube systems is given. In test tube systems specific operations are applied to the objects in their components (test tubes) in a distributed and parallel manner; the results of these computations are redistributed according to a given output/input relation using specific filters. A general theoretical framework for test tube systems is presented which is not only a theoretical basis of systems used for practical applications, but also covers the theoretical models of test tube systems based on the splicing operation as well as of test tube systems based on the operations of cutting and recombination. For test tube systems based on the operations of cutting and recombination we show that in one test tube from a finite set of axioms and with a finite set of cutting and recombination rules only regular languages can evolve

Biomimetic Membranes Realized with Arrays of Carbon Nanofibers

A microfluidic device with imbedded nanoporous membranes, constructed using a novel nanostructured material, was designed, built, modeled, and tested. The membranes were shown to be modular, and by adsorbing monodisperse latex spheres to the fibrous membrane, the pore size could be controlled. A mathematical model of the device was developed based on several existing fluidic models for transport through fibrous materials, and an image processing algorithm was designed to extract the hydrodynamic properties of the device from a series of scanning electron micrographs based on the existing hydrodynamic models. A series of experiments were performed using fluorescent microscopy to quantify the hydrodynamic properties of the device. The results of these experiments suggest that the modeling was accurate. This thesis explores several unique issues. The first is that tortuosity, defined as a particle’s path length divided by its displacement, is the factor that scales the reference diffusion. The second is that the membrane can be thought of as a realization of random fractal. The third is that tortuosity can be related to the resistance scaling factor, a property of a fractal. To support these claims, a close agreement between a classical and a fractal permeability model is shown. In addition, a model is incorporated to approximate surface effects showing that the surface cannot be categorically neglected because of the rather large device dimensions. Finally, the extrapolation of 3-dimensional information from an SEM image is used to determine the model parameters

A Risk-Based Approach to Evaluate the Impact of Interventions at Reducing the Risk of Foodborne Illness Associated with Wheat-Based Products

Pathogens are emerging on previously unrecognized food vehicles, such as wheat flour, which is a widely consumed commodity. Despite its low water activity, wheat-based ingredients and products have been implicated in several foodborne outbreaks over the last few years, resulting not only in the recall of food products but also in consumer illnesses. As a raw agricultural commodity, wheat is exposed to naturally occurring microbiological contamination that may compromise the overall safety of flour and other derived products. To address the increased concern regarding the safety of wheat-based foods, the objectives of the present research study were designed to develop and implement intervention strategies (i.e., acidic saline tempering solutions and high-pressure processing) aimed at reducing foodborne contaminants at different points along the mill-to-table continuum. Additionally, the effectiveness of such interventions at reducing public health risks was assessed using a stochastic, risk assessment model. Tempering with acidic saline solutions significantly improved the safety of wheat prior to milling, without substantially affecting the functional properties of straight-grade flour. For instance, the combination of lactic acid (5.0% v/v) and NaCl (~26% w/v) reduced the aerobic mesophilic bacteria and E. coli O157:H7 counts in soft wheat by 3.1 and 1.8 log CFU/g, respectively. A microbiological survey conducted in a commercial milling facility revealed that, as wheat is milled into flour, there is a substantial risk of cross-contamination by microorganisms potentially inhabiting the milling equipment. Appropriate cleaning and sanitization regimens should, therefore, be implemented in the mill to reduce such risk. The application of high-pressure processing (600 MPa, 6 min), as a post-packaging intervention, significantly reduced E. coli counts in cookie dough by as much as 2.0 log CFU/g, without causing significant changes on product quality parameters. The risk assessment modeling revealed that the application of these interventions along the mill-to-table continuum can significantly reduce the public health risks associated with the consumption of cookie dough contaminated with E. coli O157:H7. The findings of this study will lead to better decision-making regarding strategies that could be applied throughout the grain processing chain to safeguard consumers. Advisor: Andréia Bianchin

Seasonal Assessments of Bioregeneration in Slow Sand Filters Amended with Granular Activated Carbon

The application of slow sand filtration (SSF) has conventionally proven to be a reliable and relatively inexpensive means of producing potable drinking water for decades. As technologies in drinking water treatment continue to advance, innovations to the design and operation of slow sand filtration have the ability to transform its contribution in municipal and industrial settings. SSF amended with granular activated carbon (GAC) has been on the rise in recent decades due to its ability to improve the removal of organic material, while allowing SSF to maintain its innate treatment simplicity. A slow sand filter amended with granular activated carbon in Winthrop, Maine has demonstrated the potential to preserve the life span of the GAC sublayer for over one and a half decades. From the time when GAC was initially installed in 2005, it has not required the addition of human regenerative interferences to maintain elevated removals of organic precursor measured by dissolved organic carbon (DOC). This study aimed to investigate the biologically active components and seasonal microbial patterns within filter sublayers that may contribute to the GAC bioregenerative process. Specific goals of this study were to explore mechanisms contributing to the maintenance of GAC adsorption sites, explore impacts of seasonal temperature variations on biodegradable and non-biodegradable organic carbon removals by slow sand filters amended with GAC, and to explore impacts of seasonal temperature variations on microbial communities. Removals associated with biodegradable organic carbon (BDOC) and non-biodegradable organic carbon (BDOC) showed significant removals after several years of filter run-time, as well as differences in removals based on various GAC “ages.” Biomass and microbial community composition showed sensitivity to filter media type, location within the filter, and influence of temperature variations. Metals accumulations and content on various media showed significant accumulations of Iron on sand media and Calcium on GAC media. Results suggest calcium cation accumulation on the GAC sublayer may be correlated to higher removals of organic carbon on GAC