Deviation from panmixia via assortative mating and divergent habitat preferences

The speciation process is often viewed to start from panmictic populations. Understanding the evolutionary mechanisms that cause populations to deviate from panmixia is essential to understanding the initial stage of population divergence that may lead to speciation. My dissertation focuses on the evolution of two mechanisms that cause deviation from panmixia: assortative mating and divergent habitat preferences. The first chapter is a meta-analysis on published measures of the strength of assortative mating within natural animal populations. Results showed that deviation from panmixia via weak positive assortative mating was typical within natural animal populations, while disassortative mating was rare or absent. Results also suggested that assortative mating did not typically evolve adaptively, but instead as an incidental consequence of other mechanisms, such as spatial segregation. Divergent habitat uses are important drivers of spatial segregation. The second chapter revealed a behavioral mechanism of divergent habitat uses between parapatric lake and stream threespine stickleback populations. The results showed strong divergent rheotaxis between lake and stream fish during their breeding season. The divergence is likely to contribute to the sorting of lake and stream fish into their natal habitats and promote habitat-based assortative mating. The third chapter focused on the neuroanatomical and morphological mechanisms of rheotaxis. Results showed significant correlations between the numbers of neuromasts (functional units of the lateral line) and rheotaxis in both lab-reared and wild-caught threespine stickleback. Results also showed heritable divergence in lateral line structure between parapatric lake and stream stickleback, suggesting that divergent rheotaxis and the resulting divergent habitat uses are likely to have a heritable component. In summary, my dissertation revealed ultimate evolutionary mechanisms of assortative mating and proximate evolutionary mechanisms of divergent habitat uses. These results shed light on the understanding of the beginning of population divergence and ultimately speciation.Ecology, Evolution and Behavio

Hydrophilic polymer foam and microsphere templates for fabrication of microcellular nickel and graphene foams with energy storage applications

Hydrophilic polymer foam and microsphere templates have attracted tremendous attentions in the past decade due to their applicability in numerous areas such as catalyst carriers and mini-reactors, filtration media, carbon foam fabrication templates, thermal and electrical insulators, and tissue engineering scaffolds. Hydrophilic polymer sphere and foam templates can be used to fabricate microcellular nickel foams and graphene foams that are finding unique opportunities in energy storage applications, including battery electrodes and matrices for solar energy storage. In this study open celled hydrophilic polymer foams and microsphere templates with controllable pore size and porosity were fabricated via solid state foaming and vacuum-assisted assembling methods. Hydrophilic polymer foams were fabricated with disulfonated poly(arylene ether sulfone) (BPS) and poly(ethylene glycol) (PEG) miscible blends. Polymer microsphere templates made with PMMA, paraffin, and EAA spheres were used as templates for fabricating bulk nickel foams, which were further used as a template to fabricate graphene foams. In order to achieve bulk microcellular nickel and graphene foams, a novel electro-polishing-assisted electroless nickel (Ni) deposition process was developed to mitigate the diffusion limitation problem. Fundamental mechanisms of the proposed process were studied using a finite difference model considering both ion diffusion and chemical reaction inside the porous media. The fabricated microcellular Ni foams exhibited sufficient thermal stability and were used to fabricate three dimensional (3D) few-layer-graphene (FLG) foams using a chemical vapor deposition (CVD) method. The resulting graphene foams had a pore size less than 100 μm, density of 0.0020 g·cm⁻³, and strut wall thickness of 5 nm. The surface-to-volume ratio of the foam was 2.5×10⁵ m²·m⁻³.Materials Science and Engineerin

Compact metallic RFID tag antennas with a loop-fed method

Several compact, low profile and metal-attachable RFID tag antennas with a loop-fed method are proposed for UHF RFID systems. The structure of the proposed antennas comprise of two parts: (1) The radiator part consists of two shorted patches, which can be treated as two quarter-wave patch antennas or a cavity. (2) A small loop printed on the paper serves as the feeding structure. The small loop provides the needed inductance for the tag and is connected to the RFID chip. The input impedance of the antenna can be easily adjusted by changing loop dimensions. The antenna has the compact size of 80 mm × 25 mm × 3.5 mm, and the realized gain about -3.6 dB. The measured results show that these antennas have good performance when attached onto metallic surfaces. © 2011 IEEE.published_or_final_versio

Characterization of petrophysical properties of organic-rich shales by experiments, lab measurements and machine learning analysis

The increasing significance of shale plays leads to the need for deeper understanding of shale behavior. Laboratory characterization of petrophysical properties is an important part of shale resource evaluation. The characterization, however, remains challenging due to the complicated nature of shale. This work aims at better characterization of shale using experiments, lab measurements, and machine leaning analysis. During hydraulic fracturing, besides tensile failure, the adjacent shale matrix is subjected to massive shear deformation. The interaction of shale pore system and shear deformation, and impacts on production remains unknown. This work investigates the response of shale nanoscale pore system to shear deformation using gas sorption and scanning electron microscope (SEM) imaging. Shale samples are deformed by confined compressive strength tests. After failure, fractures in nanoscale are observed to follow coarser grain boundaries and laminae of OM and matrix materials. Most samples display increases in pore structural parameters. Results suggest that the hydrocarbon mobility may be enhanced by the interaction of the OM laminae and the shear fracturing. Past studied show that the evolution of pore structure of shale is associated with thermal maturation. However, the evolution of shale transport propreties related to thermal maturation is unclear due to the difficulty of conducting permeability measurement for shale.This work studies evolution of permeability and pore structure measurements using heat treatment. Samples are heated from 110°C to 650°C. Gas sorption and GRI (Gas Research Institute) permeability measurements are performed. Results show that those petrophysical parameters, especially permeability, are sensitive to drying temperature. Multiscale pore network features of shale are also revealed in this study. Characterizing fluids in shale using nuclear magnetic resonance (NMR) T₁-T₂ maps is often done manually, which is difficult and subjected to human decisions. This work proposes a new approach based on Gaussian mixture model (GMM) clustering analysis. Six clustering algorithms are performed on T₁1-T₂ maps. To select the optimal cluster number and best algorithm, two cluster validity indices are proposed. Results validate the two indices, and GMM is found to be the best algorithm. A general fluid partition pattern is obtained by GMM, which is less sensitive to rock lithology. In addition, the clustering performance can be enhanced by drying the samplePetroleum and Geosystems Engineerin

Stochastic Aggregation: Scaling Properties

We study scaling properties of stochastic aggregation processes in one dimension. Numerical simulations for both diffusive and ballistic transport show that the mass distribution is characterized by two independent nontrivial exponents corresponding to the survival probability of particles and monomers. The overall behavior agrees qualitatively with the mean-field theory. This theory also provides a useful approximation for the decay exponents, as well as the limiting mass distribution.Comment: 6 pages, 7 figure

Scaling and Universality in City Space Syntax: between Zipf and Matthew

We report about universality of rank-integration distributions of open spaces in city space syntax similar to the famous rank-size distributions of cities (Zipf's law). We also demonstrate that the degree of choice an open space represents for other spaces directly linked to it in a city follows a power law statistic. Universal statistical behavior of space syntax measures uncovers the universality of the city creation mechanism. We suggest that the observed universality may help to establish the international definition of a city as a specific land use pattern.Comment: 24 pages, 5 *.eps figure

Aerodynamics and motor control of ultrasonic vocalizations for social communication in mice and rats.

BACKGROUND: Rodent ultrasonic vocalizations (USVs) are crucial to their social communication and a widely used translational tool for linking gene mutations to behavior. To maximize the causal interpretation of experimental treatments, we need to understand how neural control affects USV production. However, both the aerodynamics of USV production and its neural control remain poorly understood. RESULTS: Here, we test three intralaryngeal whistle mechanisms-the wall and alar edge impingement, and shallow cavity tone-by combining in vitro larynx physiology and individual-based 3D airway reconstructions with fluid dynamics simulations. Our results show that in the mouse and rat larynx, USVs are produced by a glottal jet impinging on the thyroid inner wall. Furthermore, we implemented an empirically based motor control model that predicts motor gesture trajectories of USV call types. CONCLUSIONS: Our results identify wall impingement as the aerodynamic mechanism of USV production in rats and mice. Furthermore, our empirically based motor control model shows that both neural and anatomical components contribute to USV production, which suggests that changes in strain specific USVs or USV changes in disease models can result from both altered motor programs and laryngeal geometry. Our work provides a quantitative neuromechanical framework to evaluate the contributions of brain and body in shaping USVs and a first step in linking descending motor control to USV production

Finding ways out of congestion for the Chicago Loop : a microscopic simulation approach

Thesis (S.M. in Transportation)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering; and, (M.C.P.)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, 2009.Includes bibliographical references (p. 118-121).Over the past two decades, the City of Chicago, as many of its counterparts in the U.S., has experienced a great increase in traffic congestion, which limits regional mobility, induces a huge amount of energy waste and Greenhouse Gas emissions, and impedes economic development. Due to congestion, bus reliability and travel speed has decreased significantly. Since the demand served by the rail system in the Chicago Loop has almost met its capacity during peak hours, and the Loop area concentrates a high percentage of total bus passenger boardings, improving bus Level-of-Service (LOS) in the Loop area is crucial to enhancing passenger mobility in the City of Chicago. As a promising alternative, bus rapid transit (BRT) may reduce negative impacts of traffic congestion; however the real challenge addressed in this thesis is how to evaluate the impacts of such policies on different stakeholders (i.e., auto-drivers and bus-riders) prior to its implementation and how to inform policy-makers on sound policy decisions. In order to address the aforementioned problems, this thesis relies on the preparation of a VISSIM microscopic traffic simulation model for the Chicago Loop area, and the utilization of a GIS traffic network, traffic counts, traffic signals and the CTA bus service data. This study proposes three sets of indicators for the purpose of evaluation of the proposed schemes: 1) bus and auto travel speed, 2) bus reliability, and 3) average bus and auto delay time.(cont.) These performance indicators will serve to compare the current base case to the proposed bus improvement (e.g. BRT) scenarios. Based on the evaluation of several scenarios, this study provides practical recommendations on how to alleviate the impact of traffic congestion on buses in order to improve bus LOS in the Chicago Loop area.by Shan Jiang.M.C.P.S.M.in Transportatio